Prevention of mist formation in sulfuric acid plants



2 Sheets-Sheet l NVENTOR a ATTORNEY J. G. MELENDY MATION IN SULFURIC ACID PLANTS PREVENTION 0F MIST FOR Jan. 30, 1951 Filed March 6, 1946 JESSE G. NELENDY g/1@ Jan. 30, 1951 J G MELENDY 2,539,519

PREVENTION 'OF MIST FORMATION IN SULFURIC ACID PLANTS Filed MaIGh 6, 4194:6 2 Sheets-Sheet 2 COKE F/LTEFI T/W/VEY Patented Jan. 30, 1951 PREVENTION OF MS'I FORMATION IN SULFURIC ACID PLANTS Jesse G. Melendy, Tarrytown, N. Y., assigner to Allied Chemical & Dye Corporation, a corporation of New York Application March 6, 1946, Serial No. 652,459

7 Claims.

This invention relates to the treatment of burner gases, such as produced from sulfur or sulfide ores and other materials used in the manufacture of sulfuric acid by the contact process, to reduce corrosion of the blowers and steelY oxide produced by burning sulfurous materials, z

such as brimstone or pyrites, are prepared for treatment in the converters by passage through a dust chamber, a wet purification system, pipe cooler, coke filter and drying tower. Alternatively, the gas produced by roasting pyrites may be passed through a dust collector, waste heat boiler, cyclone dust separator and thence through the wet purification system, pipe cooler, coke filter and drying tower. The chief function of the coke filter is to remove sulfuric acid mist from the gas, which mist is produced by the partial conversion of the sulfur dioxide to sulfur trioxide in the burner, and subsequent condensation of the sulfur trioxide with the moisture in the gas stream. The removal of sulfuric acid mist minimizes corrosion of the blowers and steel piping through which the gas stream passes in its flow from the drying tower to the converter. Notwithstanding eicient operation of the coke filters to remove substantially all sulfuric acid mist formed, it has been found that corrosion of the blower which pulls the gas through the drying tower and forces it into the converter, and of the steel piping connecting the blower with the drying tower and with the converter system, takes place, requiring relatively frequent repair or replacement of these parts.

Among the objects of this invention is to provide a process of treating burner gases used in the manufacture of sulfuric acid by the contact method which process substantially minimizes or eliminates corrosion of the blower and of the gas nue connecting the dryer with the blower and of the flue connecting the blower with the subsequent equipment leading to. the converter. Other objects and advantages of this invention will be apparent from the following detailed description thereof.

The present invention is based upon certain discoveries, the foremost of which is that in the flow of the gas from the mist-remover e. g. the coke filter to the dryer, sulfuric acid mist formation takes place, which mist is not removed in the 2 the dryer and with other equipment in the train leading to the converter system, and that such mist formation can be avoided by lowering the dew-point of the gas just prior to its leaving the mist-remover to a point such that substantially no condensation of moisture takes place in the flue connecting the mist-remover with the dryer. Lowering the dew-point of the gas leaving the mist-remover, from about 1 to 7 F.-preferably from about 3-7F., prior to its entry into the ue connecting the mist-remover with the dryer, usually will be sufficient to prevent sulfuric acid mist formation in the gas iiue connecting the mist-remover with the dryer; in those cases where the gas leaves the mist-remover at a temperature of about F. above prevailing atmospheric temperature, a lowering of the dew-point of about 23F. or less, will be found adequate; if the temperature of the gas is as much as F. or more yabove the prevailing atmospheric temperature, then the dew-point should be lowered more than 3 F., say as much as 7 F.

I have further found that when using an upiiow mist-remover, such as an upiicw coke filter as frequently used, cooling of the gas inevitably takes place as it iiows through the upper portion of the device into the gas exit main, with consequent condensation of water which acts as a catalyst for the oxidation of `sulfur dioxide to sulfur trioxide, resulting in the production of sulfuric acid mist 4which is not removed in the dryer and which causes corrosion of the blower and associated steel piping. In order to prevent sulfuric acid mist formation at minimum expense .and with minimum change in existing equipment,

vof the gas stream so as toavoid sulfuric acid mist formation in the main or iiue .connecting the mist-remover with the drying tower. Lowering the dew-point'from 1 to '7 F., asabove indicated, will be found adequate to prevent sulfuric acidmist formation from taking place in this flue. 1

For convenience in describing the invention, reference is made to the accompanying drawing in which Fig. 1 represents diagrammatically a preferred layout of equipment for cooling and purifying burner gases in accordance with the present invention; Fig. 2 represents diagrammatically an alternative arrangement; and Figs. 3 and 4 are enlarged details of apparatus units of Figs. 1 and 2 respectively.

In the drawing, I'IJ'l indicates a burner or roaster for producing burner gases by the combustion of sulfurous material such as brimstone or pyrites with air. From the burner or roaster I0, the gases, either with or withoutagpartialaprecipitation of dust particles in suitable dustchambers, are conducted through a wet cooler I I consisting of one or more scrubbing towers-,where the gases are scrubbed with dilute sulfuric acid. Fromk the cooler II, the gas passes thru a down-draft pipe cooler I2. The gases lmay lenteritheewet cooler at a temperature of 700 to 1000 F. and may be cooled therein to a temperature of about V300" and may enter the pipe Cooler at this temperature and lbe vcooled by indirect heat exchange with 'water passing' onthe outsidev of the vpipe cooler'to atemperature of about 80'tof100 'In this coolerja substantial amount of water YVapor is condensedandis discharged-'from the system, 'thru a `suitable v`draw-off, as weak e.'g. 3-'4% Vsulfuric acid. `The gas from the-pipe .cooler I2 containing'sulfuric acid in'the'form of finemist produced by the' partial conversion of second, downwardly. -If.desi1'ed,.only a single doWn-draftcoke Aboxmay be used instead of the two-.boxes shown. The gases pass downwardly through thebed of -ccke showncontained in the second cokeflter. As thegases `leavethe second coke ziilter, they pass .over a body of sulfuric Yacid I ofI-I2SO4 strengthsubstantially greater ythan .the drip produced in the ,coke filter I4. Under some conditions ofoperation, thisstronger .acid maybe supplied,.for.example,by.introducing,

vproducedin cokelter-IS into .the body of acid .I5 in thebottomofoke filter I4, and'thereby Yincreasing the Vstrength ofthe acid, the acid flowing over the bottom Y,of the vcoke lter I4 in a direction counter-current vto vthe ow of Agas andbeing withdrawn fromthis ilter I4 through .line I-8. ,Instead of .introducing stronger acid from .coke filter I3 intocokebox I4, strong acid :from anextraneoussource may be supplied to the .coke lter I4. n.duced in the .drying tower or strong'acid. from For example, drying acid ypro- .anysuitable source lmaybe 'owed .over the'bot- .tomof-the coke filter I4 in adirection counter- `lcurrent to .theflowof 1gas, Vthe strength of the :acid andthe timeof contact .betweenxthe'acid andgas beingsuch as to'lower the.dew point of 'the gas stream enough'to preventsulfuric Vacid mist formation .in the flue I9 .connecting the `coke filter I4`with the .drying towerV 20.

From the coke filter 'I 4, the gas ,owsithrough drying'towerZ'D, which may be a 'conventional' drying tower in which the gas is contacted with concentrated sulfuric acid to eifect removal of moisture from the gas. From this drying tower the gas ows through a blower 2l which pulls the gas through the train of equipment hereinabove described and forces it through a heat exchanger. 22 into the-fconverterisystemj23. The structure and operation of the drying'tower 20, `blower 2 I, heat exchanger 22 and converter system 23, are conventional and hence need not be described 'in 'further detail.

'In' the 'modification of Fig. 2, the SO2 gas produced in the pyrites burner 24 is passed through a waste VVheat :boiler 25 and cyclone dust collector 2%. -The structure and operation of these units is described in detail in the prior art such, for example, as-theMacDonald Patent No. 1,985,902 of January 1, 1935. From the dust collector 26, the gas'may pass through a wet cooler 2'I similar to wet cooler I I of Fig. 1, pipe cooler 28 simi- -lar to the pipe cooler I2 of Fig. 1, and thence into-'an electrical precipitator 29 which mayfbe,

for example, a well-'known Cottrell precipitator for removing residual dustand-sulfuric acidi-mist present in the `gas stream.

In accordancewith the present invention;v the 4gas 'flows downwardly through electricalv precipitator 29, through the precipitating element not shown contained therein, and as it leaves the Aprecipitator flows over a body lof sulfuricv acid moving countercurrentto the direction of'flow vof gas over the base of the precipitator, which acid isofgreater strength than the acid drip produced in the precipitator; thestrength of the acidand the `time of Contact betweenthe acid andthe gas stream is such .as'to accomplishia lowering of the dew .point of the [gas istream adequate to prevent sulfuric acid mist formation .in -the Yflue 33.connecting electrical precipitatorj29 with the ,drying tower '32. The strong sulfuric acid may be supplied tothe bottom of precipitator 29 Afrom any suitable lsource as by an'inlet pipe 34 lopening into flue 33 at a: point adjacent the base of the precipitator, the acid being'withdrawn from the precipitator through the :draw-oli' 35. VFrom Athe drying tower 32,^the gas ows throughblower 36, vheat exchanger '3T-and converter 38,similar vto thesefunits of Fig. 1.

In the operationyofthemodification of Fig. 2

Ythe sulfur dioxide containing gas is cooled in the vthrough the drying tower 32, blower 36, heat exchanger '37 vand convertersystem 38, conditions `in lwhich `are unchanged from existing'present practice except that no sulfuric 'acid mist isy introduced into these units andthe connecting' piping `and hence corrosion 'difcu'lties sare 'avoided The strength of the acid suppliedto the ibase `cf 'the down-draft `mist-remover'will, vof course, vary, depending upon lthe temperature of the gas stream, the Astrength of the drip acid pro- "duced in the'mist-remover withwhich `the gas stream is in equilibrium,` prevailing atmospheric 'temperature conditions, etc. -Ystrength'of acidused'should'f beadequate VY'to Aac- 'In general, the

Y com'plish a lowering of the dew-point of the gas stream from 1 to '7 F., preferably from 3 to 7 F. In the operation of sulfuric acid plants of the general type to which this invention relates, the I-I2S04 strengths of the drips of the mist-remover may vary within the range of 20%, a drip having an H2SO4 strength of about being a representative average. In carrying out the invention, when it is desired to lower the dew-point of the gas stream in the gas exit iiue of the mist-remover 1 F., the pool of acid in the bottom of the down-draft mistremover should be maintained at a percent H2SO4 concentration at least 4 in excess of the percent H2SO4 concentration of the drip produced in the mist-remover'under the particular conditions of operation, that is, if a normal drip of the mist-remover has an H2504 strength of 15%, the concentration of thepool of acid in the bottom of the mist-remover should be maintained at not less than 19%. Similarly, when it is desired to lower the dew-point of the gas stream in the exit flue of the mist-remover 3 F., the percent H2804 concentration of the pool of acid in the bottom of the mist-remover should be maintained at least 11 in excess of the percent H2SO4 concentration of the drip produced, and when it is desired to lower the dew-point 7 F., the percent HzSOi concentration of the acid pooly should be maintained at least 20 in excess of the percent H2SO4 concentration of the drip.

According to one example, in operations involving the use of two coke boxes, in the iirst of which 20 B. acid drip (22.3% I-I2SO4) is produced and in the second or down-draft box 15 B. (16.4% I-IzSOi) drip is produced in quantity approximately 1A; that produced in the iirst box, the temperature of the gas leaving the second box being about 80 F., the introduction of the drip from the first box into the second where is mixes with the drip in the second and flows out of the other end of the second box in a direction countercurrent to the .flow of gas thereover, lowers the dew-point of the gas about 11/2 F., which if the flue leading to the drying tower is suitably insulated is adequate to prevent sulfuric acid mist formation in this iiue. In this instance, the HzSOi concentration of the `pool of acid in the bottom of the second box was about 21.1%. By using stronger acid and preferably supplying this stronger acid to the mist-remover so that the gas leaving the mist-remover contacts the stronger acid before the latter mixes with the drip in the coke box, the dew-point of the gas may be further reduced.

It will be noted that in accordance with the present invention, the sulfur dioxide gas leaving a down-draft mist-remover is treated to lower its dew-point so as to avoid condensation of moisture in the gas flue leading to the dryer. The condensation of moisture in this iiue, I have found, catalyzes the oxidation of sulfur dioxide to sulfur trioxide, resulting in the production of new mist which is not removed in the dryer and causes corrosion of the blower and the flues in the train. connecting the dryer with the blower `and the blower with the converter system. By preventing the condensation of moisture in the iiue connecting the mist-remover with the dryer, I have found new sulfuric acid mist formation is avoided, with consequent elimination of these corrosion diicultes.

tact process, which gas treating process involves the flow of the burner gases through a cooler,

downwardly through a coke filter comprising 1a coke bed, through a gas flue and thence through a dryer, the improvement which comprises drying the gases by flowing said gases after passage thereof through said coke bed while said gases are in said coke iilter and prior to theirvv passage through said gas ue in contact with sulfuric acid of a strength greater than the drip formed in said coke lter thereby to prevent formation of sulfuric acid mist in said gas ilue.

2. In a process of treating burner gases used in the manufacture of sulfuric acid by the contact process which gas treating process involves the flow of the burner gases through ya cooler, downwardly through an electrical precipitator comprising a precipitating element, through la gas ue and thence through a dryer, the improvement which' comprises' drying the gases by flowing said gases after passage thereof through said precipitating element, while said gases are in said precipitator and prior to their passage through said gas flue in contact with sulfuric acid of a strength greater than that formed in said precipitator thereby to prevent the formation of sulfuric acid mist in said gas flue.

3. In a process of treating burner gases used in the manufacture of sulfuric acid by the contact process, which gas treating process involves the iiow of gases through a wet cooler, pipe cooler, a down-draft coke filter comprising a coke bed, a drying tower and into a converter system, the improvement which comprises drying the gases by flowing said gases after passage thereof through said coke bed, while said gases are in said coke filter and prior to the flow of the gases through the gas iiue connecting the downdraft coke iilter with the drying tower, in countercurrent iow with a body of sulfuric acid of a strength greater than the drip produced in the coke iilter, the strength of the acid and the time of contact between the gas stream and the body of acid being sufficient to lower the dew point of the gas stream from 3 to '7 F.

4. In a process of treating burner gases produced by roasting pyrites for use in the manufacture of sulfuric acid by the contact process, which gas-treating process involves the flow of gases through a waste heat boiler, a cyclone dust collector, a wet cooler, a pipe cooler, a down-draft electrical precipitator comprising a precipitating element, a drying tower and into the converter system, the improvement which comprises drying the gases by flowing said gases after passage thereof through said precipitating` element, while said gases are in 'said electrical precipitator and prior to the flow of gases through the gas ue connecting the electrical precipitator with the drying tower, in contact with a body of sulfuric acid of a strength greater than the drip acid produced in the precipitator, the strength of the body of sulfuric acid and the time of contact between the acid and the gases being sufcient to lower the dew point of the gases from 3 to '7 F.

5. In a process of treating burner gases used atea-,ma

in: theimanufacturefo'1-sulfuricacidi by the Contact 5 process;l which" gasiltrea-ting Aprocessi involves the flow of gasesthrough'a. wet cooler, Vpipe cooler, a down-draft `coke lter comprising a coke' bed, a drying tower .andinto `a.' converter system, the improvement which comprises drying the gases by fiowing saidga'ses after-'passage thereof `ythrough sa'idl coke 'b'ed; While said gases are in said'. coke ilfter and prior. toitheow of theV gases. through thefg'as flue connecting' thedowndraft 4coke filter with the dryingtower, in countercurrent flow witha vbodyofsulfu'ric'aeid maintained at a percent HQSO@` concentration at least 4 in excess 'of the z'percent :H2S04 concentration of the dri'pproduced infsaid filter.l

6L Ia process of treating burner gases used inlthermanufacture of sulfuric a'cidbyvthe contact process, in which gas treatingV` process the gases are passed-through' a cooler, through a mistre'move'r containing a mist-removing element, through a gas flue 'and thence `through a dryer, the limprovemen'ft which comprises reducing the moisture content of the gases, after 'passage thereof through said' mistlremo-v-ing element, W'hiler sad'lgases are in v'said mist-remover`and prior to their entryinto the'gas flue connecting the mist-remover with the dryer, to fan extent suieient to lower the'deW point ofthe gases from 8P "to 7 F., thereby to avoid condensation of moisture in said'gas flue and-prevent theIorrn ation'vfof :any sulfur-ic acid 'mist in the gases prior to their entry into said` dryer.

'7. In a processortreatingfburner =gasesi-used inthe manu-facturefof'sulfuric aci-dvby the=contact process, in which gastreating processthe gases are passed through ef cooler, downwardly; through a mist-remover "containing `a"mist-rernovirig element, through a gas flue and thence througha dryer, the improvement which' com-prisesdrying the gases by owing' said gases, afterv passage thereof through said mist-removing element While'said `gases-are in said mist-remover and prior to their passa-ge through said gas-Hue, in contact with sulfuric' acid of'a strength greater than the drip -formedfin said mist-,removerfthereby lto `prevent formation of sulfuric acid-mistvn said gasue;

JESSE G.

REFERENCES CITED The following references are of record zin'the le of this patent:

UNITED STATES PATENTS'I Von GrSeWaldet al. Feb; 23, 1937 

3. IN A PROCESS OF TREATING BURNER GASES USED IN THE MANUFACTURE OF SULFURIC ACID BY THE CONTACT PROCESS, WHICH GAS TREATING PROCESS INVOLVES THE FLOW OF GASES THROUGH A WET COOLER, PIPE COOLER, A DOWN-DRAFT COKE FILTER COMPRISING A COKE BED, A DRYING TOWER AND INTO A CONVERTER SYSTEM, THE IMPROVEMENT WHICH COMPRISES DRYING THE GASES BY FLOWING SAID GASES AFTER PASSAGE THEREOF THROUGH SAID COKE BED, WHILE SAID GASES ARE IN SAID COKE FILTER AND PRIOR TO THE FLOW OF THE GASES THROUGH THE GAS FLUE CONNECTING THE DOWNDRAFT COKE FILTER WITH THE DRYING TOWER, IN COUNTERCURRENT FLOW WITH A BODY OF SULFURIC ACID OF A STRENGTH GREATER THAN THE DRIP PRODUCED IN THE COKE FILTER, THE STRENGTH OF THE ACID AND THE TIME OF CONTACT BETWEEN THE GAS STREAM AND THE BODY OF ACID BEING SUFFICIENT TO LOWER THE DEW POINT OF THE GAS STREAM FROM 3* TO 7* F. 